From aa-asterisk.org.uk wiki
Location Independent Electronic Communications Service numbers are telephone numbers designed to be used by 'new voice services' (as BT puts it). Typical examples are Voice over IP services and voice services that are not necessarily in a fixed location. (However this is not the same as 'mobile' services, which are 07 numbers.)
LIECS numbers currently begin 056 and are charged by some operators, but not all, at equivalent rates to 01/02 geographic rate calls. There is no requirement to charge these numbers at geographic rates. In the BT Price List, the official charge band for 056 numbers is g21, category 11.